Source/drain performance through conformal solid state doping

ABSTRACT

A method for improving source/drain performance through conformal solid state doping and its resulting device are disclosed. Specifically, the doping takes place through an atomic layer deposition of a dopant layer. Embodiments of the invention may allow for an increased doping layer, improved conformality, and reduced defect formation, in comparison to alternate doping methods, such as ion implantation or epitaxial doping.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. Non-provisional patent applicationSer. No. 13/504,079, filed on Sep. 17, 2012, entitled “Synthesis and Useof Precursors for ALD of Group VA Element Containing Thin Films,” andissued as U.S. Pat. No. 9,315,896, the disclosure of which is herebyincorporated by reference in its entirety.

FIELD OF INVENTION

The present disclosure generally relates to processes for manufacturingelectronic devices. More particularly, the disclosure relates to formingsource/drain devices for NMOS and CMOS applications. Specifically, thedisclosure discloses methods to improve a source/drain doping level witha conformal solid state doping technique.

BACKGROUND OF THE DISCLOSURE

Germanium has been considered as an appropriate material for use in CMOSand NMOS devices. With the trend towards smaller devices, contact areaon the devices has become smaller, with a substantial increase incontact resistance. The increase in contact resistance has beencountered with high source/drain doping.

The minimum contact resistivity on n-type Germanium has been achievedthrough antimony (Sb) ion implantation combined with laser annealing,according to Miyoshi et al., VLSI 2014, P180. However, the ionimplantation process can be challenging for FinFET and nanowire devices.

As a result, a method for improving the source/drain performance isdesired.

SUMMARY OF THE DISCLOSURE

In at least one embodiment in accordance with the invention, a method offorming a semiconductor device for source/drain applications isdisclosed. The method comprises: providing a substrate for processing ina reaction chamber, the substrate having at least one formedsource/drain region; performing a surface cleaning on the substrate, thesurface cleaning removing oxides or native oxides from the substrate;performing an atomic layer deposition of a dopant layer on thesubstrate; performing an atomic layer deposition of a capping layer onthe dopant layer; and performing a drive-in anneal step—e.g., to diffusedopant from the dopant layer into the at least one formed source/drainregion. The dopant layer can form a channel material for NMOS and CMOSdevices.

In at least one embodiment in accordance with the invention, a method offorming a semiconductor device for source/drain applications isdisclosed. The method comprises: providing a substrate for processing ina reaction chamber, the substrate having at least one formedsource/drain region; performing a surface cleaning on the substrate;performing an atomic layer deposition of a dopant layer on thesubstrate; and performing an atomic layer deposition of a capping layeron the dopant layer. The dopant layer can form a channel material forNMOS and CMOS devices.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described herein above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught or suggested herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments will becomereadily apparent to those skilled in the art from the following detaileddescription of certain embodiments having reference to the attachedfigures, the invention not being limited to any particular embodiment(s)disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the inventiondisclosed herein are described below with reference to the drawings ofcertain embodiments, which are intended to illustrate and not to limitthe invention.

FIG. 1 is a flowchart of a method in accordance with at least oneembodiment of the invention.

FIG. 2 is a flowchart of another method in accordance with at least oneembodiment of the invention.

FIGS. 3A-3C are illustrations of devices in accordance with embodimentsof the invention.

It will be appreciated that elements in the figures are illustrated forsimplicity and clarity and have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements in the figures may beexaggerated relative to other elements to help improve understanding ofillustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it willbe understood by those in the art that the invention extends beyond thespecifically disclosed embodiments and/or uses of the invention andobvious modifications and equivalents thereof. Thus, it is intended thatthe scope of the invention disclosed should not be limited by theparticular disclosed embodiments described below.

Atomic layer deposition (ALD) solid state doping (SSD) may be one way toform NMOS and CMOS devices. One reason for this may be the ability ofALD SSD to form films with excellent conformality and defect freefeatures. Alternate doping methods, such as ion implantation, mayintroduce defects that ALD SSD can avoid during conformal doping of 3-Dstructures. ALD SSD also may provide the capability to deposit thinfilms with precise sub-nanometer thickness control, which thusdetermines the dose or number of atoms available at the surface toincorporate into the semiconductor as active dopant species. Embodimentsin accordance with this invention may result in an increase of a dopinglevel near an interface with an ultra-shallow doping profile. Forexample, a doping level greater than 1×10²⁰/cm³ with a diffusion depthless than 30 nm may be preferred.

In accordance with at least one embodiment of the invention, targets forthe doping level through ALD SSD may approximately be 5×10²⁰/cm³. TheALD SSD doping level may be an order of magnitude greater than thatachieved through an alternate method, such as epitaxial doping, of5×10¹⁹/cm³. In addition, the alternate methods, such as ion implantationor epitaxial doping, may result in the morphology degradation of thefilm when incorporating high concentrations of substitutional orinterstitial dopant species into the semiconductor matrix, and renderthe film inapplicable for its intended use in CMOS or NMOS devices.

FIG. 1 illustrates a method 100 in accordance with at least oneembodiment of the invention. The method 100 may take place in a Pulsar®XP ALD reactor provided by ASM International B.V., for example.

The method 100 may include a first step 110 of source/drain (S/D)formation. The first step 110 may entail providing to a reaction chambera substrate with a source/drain (S/D) regions formed within therein orthereon. For example, the substrate may comprise germanium, silicon,silicon germanium, or other III-V materials, having source and drainregions formed therein or thereon.

The method 100 may include a second step 120 of surface cleaning. Thesecond step 120 may include a cleaning of a wafer with a cleaning agent.The effect of the second step 120 may be to remove any oxides or nativeoxides on the surface of the substrate. The presence of oxides or nativeoxides may degrade performance as it will adversely affect the contactresistivity of the substrate device.

In the second step 120, for example, a pretreatment may occur, such as agermanium wafer being cleaned with hydrofluoric acid (HF). Otherpotential cleaning agents include hydrochloric acid (HCl) or NF₃ plasma,for example. In accordance with at least one embodiment of theinvention, the second step 120 may comprise a standard wet clean thatmay take place in a Horizon module provided by ASM International B.V.,for example.

The method 100 may include a third step 130 of a dopant layer ALD. Thedopant layer deposited in the third step 130 may include antimony,boron, arsenic, phosphorus, magnesium, carbon, silicon, or sulfur, forexample. The dopant layer deposited in the third step 130 may beelemental or compound material. The third step 130 may take place at atemperature ranging between 20° C. and 450° C. The pressure in areaction chamber, for this and other deposition steps described herein,is typically from about 0.01 to about 20 mbar, more preferably fromabout 1 to about 10 mbar. However, in some cases the pressure will behigher or lower than this range, as can be determined by the skilledartisan given the particular circumstances. The third step 130 may berepeated until a desired thickness is achieved, such as 0.1 nm to 15 nm.The dopant layer may include antimony or arsenic deposited in accordancewith the disclosures of U.S. patent application Ser. No. 13/504,079,which is hereby incorporated by reference.

In accordance with at least one embodiment of the invention, adeposition of antimony may take place in the reaction chamber during thethird step 130. The temperature of the reaction chamber during the thirdstep 130 may range between 60-120° C., preferably between 60-100° C.,and more preferably between 60-80° C. The third step 130 may be repeatedas needed in order to obtain a desired thickness for the antimony layer,which in some instances may be 0.5 nm and 10 nm in other instances. Insome embodiments, the third step 130 may not form a layer; instead, whatmay be formed may be isolated locations of material or islands, possiblyseparate or partially connected, of material comprising antimony.

In order to deposit antimony, the third step 130 may include the pulsingof a first precursor comprising a metal halide, such as SbCl₃, SbF₃,SbBr₃, or SbI₃, for example. The pulsing of the first precursor mayrange in duration between 0.1 and 5 seconds, and preferably between 0.5and 2 seconds. The third step 130 may then include purging of the firstprecursor with a purge gas, such as N₂, Ar, or other inert gas. Thepulsing of purge gas may range in duration between 5 and 15 seconds, andpreferably between 5 and 10 seconds.

In order to deposit antimony, the third step 130 may include the pulsingof a second precursor comprising antimony. The second precursor maycomprise at least one of: trimethlyl silyl antimony, triethyl silylantimony, antimony alkoxides, or antimony amides, for example. Thesecond precursor may also comprise antimony bound to silicon atomshaving a general formula of Sb(AR¹R²R³)₃, where A is Si or Ge and R¹,R², and R³ are alkyl groups comprising one or more carbon atoms. Thepulsing of the second precursor may range in duration between 0.1 and 5seconds, and preferably between 0.5 and 2 seconds. The third step 130may then include purging of the second precursor with a purge gas, suchas N₂, Ar, or other inert gas. The pulsing of purge gas may range induration between 5 and 15 seconds, and preferably between 5 and 10seconds.

The method 100 may include a fourth step 140 of a capping layer ALD. Thelayer deposited in the fourth step 140 may include silicon dioxide(SiO₂), silicon nitride (SiN), aluminum nitride (AlN), titanium nitride(TiN), silicon-containing carbon, or aluminum oxide (Al₂O₃), forexample. The fourth step 140 may take place at a temperature rangingbetween 20° C. and 450° C. The capping layer deposition may not resultin oxidation of the dopant layer formed in the third step 130.

For example, to form a layer of silicon dioxide, the fourth step 140 mayinclude the pulsing of a first precursor comprising at least one ofsilane, disilane, trisilane, amino silane, or amino disilane, forexample. The pulsing of the first precursor may range in durationbetween 0.1 and 5 seconds, and preferably between 0.5 and 2 seconds. Thefourth step 140 may also include purging of the first precursor using apurge gas, such as N₂, Ar, or other inert gas. The pulsing of the purgegas may range in duration between 0.1 and 30 seconds, and preferablybetween 0.3 and 3 seconds.

The fourth step 140 may also include the pulsing of a second precursorcomprising at least one of oxygen (O₂) plasma, ozone (O₃), water (H₂O),oxygen (O₂), hydrogen peroxide (H₂O₂), or other oxygen precursor. Thepulsing of the second precursor may range in duration between 0.1 and 5seconds, and preferably between 0.5 and 2 seconds. The fourth step 140may then include a subsequent purging of the second precursor using thepurge gas. The pulsing of the purge gas may range in duration between0.01 and 15 seconds, and preferably between 0.05 and 2 seconds. Similarto the third step 130, the fourth step 140 may be repeated as necessaryin order to form a layer having a desired thickness. In some instances,a bi-layer structure may be used for the fourth step 140, for example, aSiN/SiO₂ structure.

The method 100 may include a fifth step 150 of a drive-in anneal, whichmay be used to drive a dopant from the dopant ALD layer into the sourceand/or drain regions. During this step, the substrate may be subjectedto a temperature range between 450° C. and 1100° C., resulting inimproved dopant drive-in. The annealing may have a duration rangingbetween 1 s and 30 minutes.

The annealing in the fifth step 150 may play an important role in anoverall thermal budget of the method 100. The overall thermal budget maydetermine a dopant diffusion depth of 30 nm, for example.

One issue solved by steps in accordance with the invention may be asolubility of the dopant. For example, there have been issues with lown-type dopant solubility in germanium. The third step 130 may allow forappropriate doping due to its improved conformality as well as itsability to limit the formation of defects due to ion implantation. Witha drive-in anneal, deposition of a solid state dopant by ALD may allowfor conformal 3-D doping of interfaces, which may not be possible in ionimplantation. In addition, the defect formation resulting from otherdoping techniques may be avoided by ALD SSD.

The method 100 may include an optional sixth step 160 of a cap layerremoval. The cap layer removal may be accomplished with an etching step,using hydrofluoric acid (HF), for example, as an etching agent.

In some instances, the cap layer removal may not be required. A drive-inanneal may obviate the need for the removal of the cap layer, if, forexample, a conventional contact metal stack of Ti/TiN can serve as a caplayer to prevent dopant out diffusion.

FIG. 2 illustrates a method 200 in accordance with at least oneembodiment of the invention. The method 200 may include a first step 210of source/drain (S/D) formation. The first step 210 may entail providingto a reaction chamber a substrate with a source/drain (S/D) formedwithin or on the substrate. For example, the substrate may comprisegermanium, silicon, silicon germanium, or a III-V material, for example.

The method 200 may include a second step 220 of surface cleaning. Thesecond step 220 may include a cleaning of a wafer with a cleaning agent.The effect of the second step 220 may be to remove any oxides or nativeoxides on the surface of the substrate. The presence of oxides or nativeoxides may degrade performance as it will adversely affect the contactresistivity of the substrate device.

In the second step 220, for example, a germanium silicon wafer may becleaned with hydrofluoric acid (HF). Other potential cleaning agentsinclude hydrochloric acid (HCl) or NF₃ plasma, for example. Inaccordance with at least one embodiment of the invention, the secondstep 120 may comprise a standard wet clean that may take place in aHorizon module provided by ASM International B.V., for example.

The method 200 may include a third step 230 of a dopant layer ALD. Thedopant layer deposited in the third step 230 may include antimony,boron, arsenic, phosphorus, magnesium, carbon, silicon, or sulfur, forexample. The third step 230 may take place at a temperature rangingbetween 20° C. and 450° C. The third step 230 may be repeated until adesired thickness is achieved, such as 0.1 nm to 15 nm.

In accordance with at least one embodiment of the invention, adeposition of antimony may take place in the reaction chamber during thethird step 230. The temperature of the reaction chamber during the thirdstep 230 may range between 60-120° C., preferably between 60-100° C.,and more preferably between 60-80° C. The third step 230 may be repeatedas needed in order to obtain a desired thickness for the antimony layer,which in some instances may be 0.5 nm and 10 nm in other instances.

In order to deposit antimony, the third step 230 may include the pulsingof a first precursor comprising a metal halide, such as SbCl₃, SbF₃,SbBr₃, or SbI₃, for example. The pulsing of the first precursor mayrange in duration between 0.1 and 5 seconds, and preferably between 0.5and 2 seconds. The third step 230 may then include purging of the firstprecursor with a purge gas, such as N₂, Ar, or other inert gas. Thepulsing of purge gas may range in duration between 5 and 15 seconds, andpreferably between 5 and 10 seconds.

In order to deposit antimony, the third step 230 may include the pulsingof a second precursor comprising antimony. The second precursor maycomprise at least one of: trimethlyl silyl antimony, triethyl silylantimony, antimony alkoxides, or antimony amides, for example. Thesecond precursor may also comprise antimony bound to silicon atomshaving a general formula of Sb(AR¹R²R³)₃, where A is Si or Ge and R¹,R², and R³ are alkyl groups comprising one or more carbon atoms. Thepulsing of the second precursor may range in duration between 0.1 and 5seconds, and preferably between 0.5 and 2 seconds. The third step 230may then include purging of the second precursor with a purge gas, suchas N₂, Ar, or other inert gas. The pulsing of purge gas may range induration between 5 and 15 seconds, and preferably between 5 and 10seconds.

The method 200 may include a fourth step 240 of a capping layer ALD. Thecapping layer deposited may comprise a metal. The metal deposited in thefourth step 240 may include titanium, titanium nitride (TiN), titaniumsilicide (TiSi_(x)), tantalium silicide (TaSi_(x)), or niobium silicide(NbSi_(x)), for example. The fourth step 240 may include the pulsing ofa first precursor comprising a metal halide, such as titanium chloride(TiCl_(x)), tantalum fluoride (TaF_(x)), niobium fluoride (NbF_(x)), orother metal halide, for example. Depending on the capping layer, thetiming of pulses may differ. For example, in order to form a silicide,the pulsing of the first precursor may range in duration between 0.01and 5 seconds, or preferably between 0.5 and 1 second. To form anitride, the pulsing of the precursor may range in duration between 0.01and 20 seconds, or preferably between 1 and 15 seconds. The fourth step240 may include the pulsing of a purge gas, such as N₂, Ar, or otherinert gas. The pulsing of purge gas may range in duration between 5 and30 seconds, and preferably between 5 and 10 seconds.

The fourth step 240 may include the pulsing of a second precursor suchas ammonia (NH₃) or silane, for example. The pulsing of the secondprecursor may range in duration between 0.01 and 30 second, orpreferably between 1 and 15 seconds. The fourth step 240 may include thepulsing of a purge gas, such as N₂, Ar, or other inert gas. The pulsingof purge gas may range in duration between 5 and 30 seconds, andpreferably between 5 and 10 seconds.

The fourth step 240 may take place at a temperature ranging between 20°C. and 600° C., preferably between 200 and 500° C., and more preferablybetween 300 and 400° C. The fourth step 240 may be repeated until adesired thickness of the capping layer is achieved, such as 0.1 nm to 5nm, preferably between 0.1 to 3 nm or 0.1 to 2 nm. The thickness of thecapping layer may be less than approximately 5 nm, less thanapproximately 3 nm, less than approximately 2 nm, or preferably lessthan approximately 1.5 nm.

The method 200 may include a fifth step 250 of a drive-in anneal. Duringthis step, the substrate may be subjected to temperatures at temperaturerange between 450° C. and 1100° C., resulting in improved dopantdrive-in. The annealing may have a duration ranging between 1 s and 30minutes.

FIG. 3A illustrates a device in accordance with at least one embodimentof the invention. The formed device may comprise a capping layer 310, adopant layer 320, and a substrate 330. At this point, a capping layer310 has been deposited, but each of the layers is distinct and separate.In addition, a drive-in anneal has not yet taken place. The dopant layer320 may comprise antimony, while the substrate 330 may comprisegermanium.

FIG. 3B illustrates a device in accordance with at least one embodimentof the invention after a drive in-anneal has taken place. The device hasa capping layer 310 and the substrate 330, but the dopant hasinfiltrated a portion of the substrate 330 to form a doped substratelayer 340. For example, if the dopant is antimony and the substrate isgermanium, the doped substrate layer 340 would comprise anantimony-doped germanium layer.

FIG. 3C illustrates a device in accordance with at least one embodimentof the invention after a drive in-anneal has taken place. Like thedevice in FIG. 3B, a drive-in anneal has taken place, but in this casehas not resulted in a complete infiltration of the dopant into thesubstrate 330. The device may comprise the capping layer 310, thesubstrate 330, and a doped substrate layer 340, but also includes adopant layer 320 representing dopant that has not infiltrated into thesubstrate 330.

The particular implementations shown and described are illustrative ofthe invention and its best mode and are not intended to otherwise limitthe scope of the aspects and implementations in any way. Indeed, for thesake of brevity, conventional manufacturing, connection, preparation,and other functional aspects of the system may not be described indetail. Furthermore, the connecting lines shown in the various figuresare intended to represent exemplary functional relationships and/orphysical couplings between the various elements. Many alternative oradditional functional relationship or physical connections may bepresent in the practical system, and/or may be absent in someembodiments.

It is to be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. Thus, the various acts illustrated may beperformed in the sequence illustrated, in other sequences, or omitted insome cases.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various processes,systems, and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

We claim:
 1. A method of forming a semiconductor device for source/drainapplications comprising: providing a substrate for processing in areaction chamber, the substrate having at least one formed source/drainregion, the at least one formed source/drain region being free of oxidesor native oxides; performing an atomic layer deposition of an elementaldopant layer on the substrate; and performing an atomic layer depositionof a capping layer on the elemental dopant layer; wherein, after theatomic layer deposition of the capping layer, the semiconductor deviceis subject to a drive-in anneal step to diffuse dopant from theelemental dopant layer into at least one of the formed source/drainregions, and wherein the atomic layer deposition of the elemental dopantlayer forms a channel material of an NMOS device with a doping levelgreater than 1×10²⁰/cm³ with a diffusion depth less than 30 nm in thesubstrate.
 2. The method of claim 1, further comprising: removing thecapping layer.
 3. The method of claim 1, wherein the substrate comprisesat least one of: silicon, germanium, silicon germanium, or a III-Vmaterial.
 4. The method of claim 1, wherein the elemental dopant layercomprises antimony, boron, arsenic, phosphorus, magnesium, carbon,silicon, or sulfur.
 5. The method of claim 1, wherein the capping layercomprises at least one of: silicon dioxide (SiO₂), titanium nitride(TiN), silicon nitride (SiN), aluminum nitride (AlN), silicon-containingcarbon, or aluminum oxide (Al₂O₃).
 6. The method of claim 1, whereinperforming the atomic layer deposition of the elemental dopant layercomprises: pulsing a first precursor onto the substrate, wherein thefirst precursor is at least one of: SbCl₃, SbF₃, SbI₃, SbBr₃, or a metalhalide; purging the first precursor from the reaction chamber with apurge gas, wherein the purge gas comprises at least one of: N₂, Ar, oran inert gas; pulsing a second precursor onto the substrate, wherein thesecond precursor is at least one of: trimethyl silyl antimony ortriethyl silyl antimony; and purging the second precursor from thereaction chamber with the purge gas.
 7. A method of forming asemiconductor device for source/drain applications comprising: providinga substrate for processing in a reaction chamber, the substrate having aformed source/drain, the substrate being free of oxides; performing anatomic layer deposition of an elemental dopant layer on the substrate;and performing an atomic layer deposition of a capping layer on theelemental dopant layer, wherein the atomic layer deposition of theelemental dopant layer forms a channel material of an NMOS device with adoping level greater than 1×10²⁰/cm³ with a diffusion depth less than 30nm in the substrate.
 8. The method of claim 7, wherein the substratecomprises at least one of: silicon, germanium, silicon germanium, or aIII-V material.
 9. The method of claim 7, wherein the elemental dopantlayer comprises antimony, boron, arsenic, phosphorus, magnesium, carbon,silicon, or sulfur.
 10. The method of claim 7, wherein the capping layercomprises at least one of: titanium, titanium nitride (TiN_(x)),titanium silicide (TiSi_(x)), tantalum silicide (TaSi_(x)), and niobiumsilicide (NbSi_(x)).
 11. The method of claim 7, wherein a drive-inanneal is performed on the substrate at a temperature greater than 400°C.
 12. The method of claim 7, wherein performing the atomic layerdeposition of the elemental dopant layer comprises: pulsing a firstprecursor onto the substrate, wherein the first precursor is at leastone of: SbCl₃, SbF₃, SbI₃, SbBr₃, or a metal halide; purging the firstprecursor from the reaction chamber with a purge gas, wherein the purgegas comprises at least one of: N₂, Ar, or an inert gas; pulsing a secondprecursor onto the substrate, wherein the second precursor is at leastone of: trimethyl silyl antimony or triethyl silyl antimony; and purgingthe second precursor from the reaction chamber with the purge gas. 13.The method of claim 7, wherein performing the atomic layer deposition ofthe capping layer comprises: pulsing a first precursor onto thesubstrate, wherein the first precursor is at least one of: TiCl_(x),TaF_(x), NbF_(x), or a metal halide; purging the first precursor fromthe reaction chamber with a purge gas, wherein the purge gas comprisesat least one of: N₂, Ar, or an inert gas; pulsing a second precursoronto the substrate, wherein the second precursor is at least one of:ammonia (NH₃) or silane; and purging the second precursor from thereaction chamber with the purge gas.
 14. The method of claim 1, whereina doping level in one or more of the source/drain regions is about5×10²⁰/cm³.
 15. The method of claim 7, wherein a doping level in one ormore of the source/drain regions is about 5×10²⁰/cm³.
 16. The method ofclaim 1, wherein the drive-in anneal is performed at a temperaturegreater than 400° C.